Liquid helium, due to its inertness and to its extremely low temperature is a very valuable specialty product for such uses as a coolant for superconductivity applications, and for laboratory research.
A major cost in the production of liquid helium is the power requirement to liquefy the helium. For example, in a liquefaction process employing work expansion of recirculating helium to produce liquid helium, a major cost is the power required to compress the vapor. It is thus desirable to have a process for producing liquid helium wherein compression power requirements are reduced.
A significant amount of helium is often present in natural gas reservoirs. Accordingly, helium can be obtained as a byproduct of natural gas production, including processing of natural gases that contain nitrogen. The nitrogen may be naturally occurring and/or may have been injected into a reservoir as part of an enhanced oil recovery (EOR) or enhanced gas recovery (EGR) operation. Because of the relative volatilities of these gases, helium, which may be present with the natural gas, concentrates in the nitrogen as the nitrogen and methane are separated in a cryogenic nitrogen rejection unit (NRU). The helium may be available from the NRU at a high enough concentration to justify further concentration and recovery. When this threshold concentration is present it would be highly desirable to employ the refrigeration inherent in the nitrogen-helium stream from the NRU to reduce the power requirements for the production of liquid helium.
Accordingly it is an object of this invention to provide a process for the more efficient production of liquid helium.
It is a further object of this invention to provide a process wherein refrigeration in a helium-containing vapor is employed to reduce the power requirements for the production of liquid helium.